Adjustable hysteresis clutch and brake

ABSTRACT

This hysteresis type magnetic device has a permanent magnet secured between two magnetizable pole members on a sleeve which is rotatably mounted on the output shaft coaxially thereof. One pole member is disposed within the other and has a plurality of axially extending external teeth or poles which confront but are radially spaced from a like plurality of internal teeth or poles on the outer pole member. A magnetizable, cup-shaped rotor is secured to the output shaft and has its annular wall projecting into the radial space between the inner and outer poles. The outer pole member is angularly adjustable relative to the inner to vary the angular separation between inner and outer poles, respectively, and hence to vary the transmittable torque in continuous slip braking and continuous or zero slip clutching connections.

United States Patent Duncan [54] ADJUSTABLE HYSTERESIS CLUTCH AND BRAKE[72] Inventor: John E. Duncan, 70 Gardenville Parkway West, Buffalo,N.Y. 14224 [22] Filed: Feb. 3, 1971 [21] Appl. No.: 112,243

[52] U.S. Cl. ..3l0/ 105 [51] lnLCl. ..H02lt 49/02 [58] Field of Search..310/92, 93, 96, 99, 166,

[56] References Cited UNITED STATES PATENTS 2,912,607 11/1959 Duncan ..310/103 3,027,472 3/1962 Galtz ..3 10/105 3,488,536 1/1970 Baermann..310/105 3,209,184 9/ 1965 Woodward ..3 10/ 103 l/1968 Jaeschke.310/105 isi 3,700,941

[ Oct. 24, 1972 Cohen ..310/1os Cohen ..3 10/96 Primary Examiner-R.Skudy Attorney-Shlesinger, Fitzsimmons & Shlesinger [57] ABSTRACT Thishysteresis type magnetic device has a permanent magnet secured betweentwo magnetizable pole members on a sleeve which is rotatably mounted onthe output shaft coaxially thereof. One pole member is disposed withinthe other and has a plurality of axially extending external teeth orpoles which confront but are radially spaced from a like plurality ofinternal teeth or poles on the outer pole member. A magnetizable,cup-shaped rotor is secured to the output shaft and has its annular wallprojecting into the radial space between the inner and outer poles. Theouter pole member is angularly adjustable relative to the inner to varythe angular separation between inner and outer poles, respectively, andhence to vary the transmittable torque in continuous slip braking andcontinuous or zero slip clutching connections.

8 Claims, 7 Drawing Figures PATENTEB BT H Z I 3.700.941

SHEET 1' UP 3 46 F INVENTOR. E JOHN E. DUNCAN ATTORNEYS PATENTEUIIII 24I972 MAX.

TORQUE HYSTERESIS/ INCIPIENT SHEET 2 [IF 3 CURVED LINE INDICATESCOMPOSITE TORQUE INCREASES WITH SLIPPAGE r COMPOSITE TORQUE ACTIVEHYSTERESIS MINIMUM AT MAXIMUM HYSTERESIS TORQUE INDEXED IPOSITION 2COMPOSITE TORQUE MAXIMUM AT MINIMUM X TORQUE INDEXED POSITION Ix EDDY ISPROPORTION- MIN.

--ZERO SLIP-*- CURRENT} MAX. TORQUE ALTO SLIPPAGE -CONTINUOUS SLIP iTORQUE INCIDENCE X. ,X ARE PRESET TORQUE ADJUSTMENTS FIG. 3

INVENTOR. JOHN E. DUNCAN ATTORNEYS PATENTEII 24 I97? 3. 700.941

sum 3 OF 3 so I (PERCENT) AIBICIDIEIFIGI I I I |0O- i I I o I I I li.280 48 I.s I 96 6.4 3.2 ABCDEFGH I -ANGULAR DISPLACEMENT I BETWEEN INNERAND 80 l I OUTER POLE FACES- so I x. TO x2 Is LINEAR PORTION OF CURVETORQUE (PERCENT) 40 FIG. 7 2o I I I AlBlCiDEiFGIH INVENTOR. I I I I I II I I JOHN E. DUNCAN ABCDEFGHIJKLMNO BY g 77/ I fl'" 7 ,29,, "I(INCREMENTS) ATTORNEYS ADJUSTABLE IIYSTERESISCLUTCII AND BRAKE Thisinvention relates to torque limiting devices, such as brakes andclutches, and more particularly to permanently magnetized hysteresismeans for continuous slip brake and continuous or zero slip clutchapplications requiring limitable torque.

It is well known that brakes and clutches may be of the permanent magnetvariety, the electromagnetic variety, or combinations thereof, that is,brakes and clutches intended for wholly magnetic slip use may be of thepermanent magnetized, magnetized eddy current and hysteresis variety, ofcombinations of both. Electromagnetic torque limiting clutches andbrakes have found much favor because they can be adjusted readily andprecisely merely by controlling the power supply to the electrical coil,or coils, that develop the magnetic fields in these devices. Moreover,they can be made to handle extremely high torque loads.

However, electromagnetic clutches have the disadvantage that they mustbe connected to electrical power supplies in order to operate. Moreover,the overall cost of these devices is increased by the need for the wirecoils, which developthe magnetic field, special mounts and housings forthese coils, and slip rings, or the like, for connecting the coils to apower supply.

Furthermore, eddy current means are incapable of zero slip operationbecause slippage is essential to torque procurement. The eddycurrenttorque derives wholly from current shunting that electrically heats therotor means and as a result decreases eddy current flow and slippagetorque as the heating of the rotor increases electrical (flow)resistance.

It is an object of this invention to provide a substantially wear free,continuous slip torque limiting device for transmitting torque by meansof a non-wearing magnetic coupling variable over a broad range oftorque.

More specifically, it is an object of this invention to provide improvedmagnetic brakes and clutches of the permanently magnetized variety,which requires no outside power source for its operation, issubstantially temperature insensitive, and is extremely reliable in bothhigh and low torque applications.

A further object of this invention is to provide magnetic brakes andclutches of the type described, which can readily and accurately beadjusted to vary the torque transmittable by the clutch from a drivingto a driven member.

A more specific object of this invention is to provide an improvedpermanent magnetic clutch having confronting, circumferential poleswhich are angularly adjustable relative to one another to vary thehysteresis of the clutch, hence the torque transmittable thereby.

Another object of the invention is to provide a brake or clutchemploying optimum high resistance rotors inhibiting eddy current flowand procuring hysteresis torque via torque displaced magnetic linkages.

Another object of this invention is to provide preinstallation and postinstallation adjustable permanently magnetized brakes and clutches.

Another object of the invention is to provide hysteresis brake andclutch apparatus employing minimal inertia brake input and clutch outputcoupling or mounting means.

Still another object of this invention is to provide magnetic clutch andbrake apparatus that achieves hysteresis torque via torque displaced ortorque distorted magnetic linkages which link through rotor means.

Other objects of the invention will be apparent hereinafter from thespecification and from the recital of the appended claims, particularlywhen read in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a fragmentary part side elevational, part axial sectional viewof a magnetic hysteresis clutch made in accordance with one embodimentof this invention;

FIG. 2 is a sectional view taken along the line 2-2 in FIG. 1 looking inthe direction of the arrows, with a portion of the clutch rotor beingbroken away for purposes of illustration;

FIG. 3 is a diagram illustrating the sequence of incipient torques,active hysteresis torques, and composite torques obtained with a brakeor clutch built according to this invention, and illustrates that theeddycurrent torque portion of a composite torque decreases as thehysteresis torque is increased;

FIG. 4 is a fragmentary axial sectional view of a modified form ofclutch adaptable to brake applications;

FIG. 5 illustrates fragmentarily and schematically a way in which abrake or clutch can be modified to employ dual rotors rather than asingle rotor;

FIG. 6 is a diagram applying to FIG. 1 and illustrating the percent ofchange in transmittable torque which is effected by incrementaladjustment of the clutch; and

FIG. 7 is a torque percentage diagram illustrating optional (lineartorque and maximal incremental torque) indexing.

Referring now to the drawings by numerals of reference, 10 denotesgenerally a continuous and zero slip clutch mounted on an inner sleeve12, which is fastened to an output shaft 14 and which preferably is madeof a non-magnetic material. Mounted to rotate coaxially about sleeve 12on conventional, axially spaced, anti-friction bearings 16 and 17, is anon-magnetic sleeve 18. Bearings 16 and 17 seat in counterbores 19formed in opposite ends of this sleeve. A conventional snap ring 20retains bearing 16 against movement in one direction on sleeve 12.

At its left end (FIG. 1) sleeve 18 is integral with a gear 22, which isdriven by a gear 24, that is fastened to drive shaft 26.

Fastened to the opposite end of the sleeve 18 for rotation therewith isa magnetizable inner pole member 28. On its outer periphery member 28has a plurality of axially extending grooves 29, which are equiangularlyspaced from one another, and which define a plurality of equiangularlyspaced externally projecting salient poles 30.

Secured to and surround the sleeve 18 intermediate its ends, andabutting the inner or left-hand face (FIG. 1) of the member 28, is anannular permanent magnet 32. The outer diameter of magnet 32 is lessthan that of the member 28, so that the teeth 30 on member 28 projectradially beyond the outer periphery of the magnet.

Secured to and surrounding the sleeve 18 between magnet 32 and gear 22,with its open end surrounding magnet 32, is a magnetizable member 34.Adjacent its closed or left end in FIG. 1, member has in its outerperipheral surface one or more radial holes 36, which are the externalreference for one or more reference holes 38 formed in member 34adjacent holes 36. Holes 38 are equal in number to, and axially alignedwith, holes 36. Adjacent its opposite or open end (the right end inFIG. 1) member 34 is formed with a circumferential groove 37 which isV-shaped in cross section.

Mounted for rotational angular adjustment around the open end of member34 is an adjustable collar or outer pole member 40. A setscrew 42 (FIG.1), which threads into a radial hole in pole member-40, projects at itsinner end into groove 37 in member 34 to secure collar 40 against axialand radial movement on member 34, while permitting the collar to berotated relative to member 34, when screw 42 is loosened. Collar 40extends axially beyond the open end of member 34; and this extendingportion of the collar is provided with a plurality of axially extending,equiangularly spaced grooves 44, which define angularly-spaced internalsalient poles 45. These salient poles are radially spaced outwardly fromthe salient poles on inner pole member or ring 28.

Adjacent its left end, collar has therethrough a plurality of angularlyspaced radial holes 46, each of which is capable of registering radiallywith the reference hole 38 in member 34 upon proper angular adjustmentof collar 40. The holes 46 are used to adjust the angular relationshipbetween the salient poles 30 and on the inner and outer pole members,respectively.

Press fit on the right end (FIG. 1) of sleeve 12 is a hub 50. At itsinner end hub 50 has a reduced-diameter portion 51, which seats againstthe ball bearing 17 to secure the latter on sleeve 12. Hub 50, and thesleeve 12, are fastened to the shaft 14 by setscrews 52, which threadthrough registering apertures 53 and 54in bushing 50 and sleeve 12,respectively, into contact with output shaft 14. The set-screwcooperates with snapring 20, 50, bearings 16 and 17, and thenon-magnetic field member 18 to retain sleeve 12 and thus the wholeassembly on shaft 14.

Mounted on hub 50, and fastened thereto by screws 56 is a generallycup-shaped rotor 58, which is made from a magnetizable material havinghigh hysteresis characteristics. The open end of rotor 58 surrounds thesalient poles of member 28, and the annular wall portion 59 of thisrotor rotates in the space between the confronting poles 30 and 45,respectively, of the two pole members.

As previously noted, the inner pole member 28, and the supporting fieldmember 34 for the outer pole member 40, are both fixed on sleeve 18.This maintains the reference hole 38 in angular registry with themidpoint of one of the inner poles 30 (the uppermost in FIG. 2) onmember 28. The angular position of poles 45 on the outer pole member 40can be adjusted relative to hole 38 by rotating collar 40 relative tomember 34 until a preselected one of the openings 46 in collar 40 isbrought into registry with bore 38.

In FIG. 2 the openings 46 in the collar 40, here shown as eight, aredesignated A, B, C, D, E, F, G and H. On each of the inner and outerpole members 28 and 40, respectively, the associated poles 30 and 45,

respectively, are equiangularly spaced from one another about the axisof sleeve 12, as are the associated grooves 29 and 44, respectively. Ifas shown in FIG. 2 the collar 40 is adjusted so that the first of itsindex apertures 46 (opening A) is disposed in registry with thereference hole 38, the inner poles 30 will register, approximately, withthe grooves 44 on the outer pole member 40. This corresponds to themaximum angular separation of inner poles 30 relative to outer poles 45,so that the magnetic lines of flux developed by the permanent magnet 32between the inner and outer poles 30 and 45 are concentrated at andbetween the confronting faces of these poles. In this position of collar40 the magnetic flux lines extending between the inner and outer poleshave, therefore, their greatest effect on the intervening wall 59 ofrotor 58, so that when the drive shaft 26 causes the inner and outerpole members 28 and 40 to be rotated in either direction, the magneticflux lines extending between the poles of these members transmit maximumpossible torque to rotor 58, and therefore to output shaft 14.

To reduce the torque transmittable by the clutch, the outer pole memberor collar 40 is rotated on member 34 to reduce the angular distanceseparating the inner and outer poles 30 and 45, or in other words, toplace the faces of these poles more nearly in registry with one another.As the faces of poles 30 and 45 approach angular registry, the fluxlines connecting the pole faces tend more and more to becomeconcentrated between the partly confronting faces of the poles untilfinally, when the faces of the inner poles 30 are in substantial angularregistry with the faces of poles 45, the hysteresis etfect of the fluxlines through the rotor 58 is reduced to a minimum, to reduceaccordingly the transmittable torque to a minimum.

In the embodiment of the invention shown in FIG. 2, the index openings46 (A through H) are angularly separated 43.4 from one another about theaxis of sleeve 12. This angular separation is l.6 less than twice theangular distance (225) separating successive recesses 44 in outer polemember 40. Consequently, when the collar 40 is rotated clockwise fromits position illustrated in FIG. 2, so as to place index opening Binstead of aperture A, in registry with the reference hole 38, the facesof the inner and outer poles 30 and 45 will be 1.6 closer to registrywith one another. As each successive opening 46 (C through H) is rotatedinto registry with the reference hole 38, the outer poles 45 are shiftedl.6 closer to full registry with the inner poles 30, until, when theindex opening H is positioned above and in registry with the referencebore 38, the inner and outer poles 30 and 45 are approximately in fullregistry with one another, so that minimum torque is transmitted to therotor 58. In FIG. 3, x, denotes the minimum preset torque adjustment,and x designates the maximum preset torque adjustment. As indicated onthe diagram the eddy current torque is proportional to the indexedposition of part 40 and to slippage.

This replacement between the transmitted torque and the angulardisplacement between the inner and outer poles 3t and 45 is illustratedgraphically in FIGS. 3 and 6. These diagrams show the incrementaltorques obtained and that composite (eddy-current and hysteresis)torques have the highest percentages of eddy currents when the magneticpoles are aligned face to face, and minimal percentages when obtuselyaligned. Moreover, the diagram of FIG. 3 shows the order of torqueprocurement. An incipient hysteresis torque is first used, followed byan active hysteresis torque, and then by a composite torque. Thisdiagram also shows that an active hysteresis torque is equal to a peakincipient hysteresis torque, that an active hysteresis torque isunaffected by change in slippage velocity, and that an eddy currenttorque (or composite torque) is affected by a change in slip velocity.

In use, the collar 40 is first adjusted to set the clutch for thedesired torque that is to be transmitted from output shaft 14. This isdone by loosening the screw 42, and rotating collar 40 until the desiredindex opening 46 is in registry with the reference hole 38, after whichscrew 42 is tightened again to hold collar 40 against rotation on member34. When torque is then applied to the input shaft 26, it is transmittedthrough pinion 24 and gear 22 to sleeve 18, and consequently to theinner and outer pole members 28 and 40. The magnetic field developed bymagnet 32 between the adjustable poles 30 and 45 magnetically grips theannular wall portion 59 of the rotor 58. The output shaft 14 is thusrotated with zero slippage or continuous slippage at the torques theclutch 10 is capable of transmitting until the load thereon exceeds theclutch torque transmission, at which time the magnetic coupling betweenpoles 30, 45 and the rotor 58 is overcome, and shaft 14 stops, while thepole members 28 and 40 continue to be rotated by input shaft 26. I

To adjust the collar 40 on the member 34 two cylindrical pins (notillustrated) may be employed. One of the pins is inserted into one ofthe holes 36, and the other into that hole 46 which is to be moved intoregistry with the reference hole 38. The pin in hole 36 is used to holdthe member 34 against angular rotation while the other pin is being usedto rotate collar 40.

Referring now to FIG. 4, .wherein like numerals are employed todesignate elements similar to those employed in the first embodiment, l0designates a modified magnetic clutch that is adaptable in brakeapplications and in which a sleeve 60 is mounted onantifriction bearings16 and 17 to rotate coaxially about the sleeve 12. As in the case of thefirst embodiment, ring 60 is press fit, or otherwise secured, in thebores of the surrounding members 28, 32 and 34, so that the latterrotate with the ring 60.

Unlike sleeve 18 in the first embodiment, however, wherein gear 22 isintegral with the sleeve, the sleeve 60 is pressed into members 28 and34. 62 denotes a detachable, non-magnetic gear, which is piloted by thebearing 16 that is retained by snap-ring 20, sleeve 12, and sleeve 60.As shown, the gear 62 is secured to the outer face of member 34 bescrews 63, only one of which is illustrated in FIG. 4. In a clutchapplication, the input torque is transmitted by the gear 62 and screws63 to member 34. Clutch 10' is otherwise identi cal in construction andoperation with clutch 10. In a brake adaption, the gear 62 is omittedand the member 34 is secured to a fixed support, such as a bulkhead 67,by screws 63.

FIG. 5 illustrates schematically a further modification of the magneticdevice shown in FIGS. 1 and 2.

Here, a pair of axially spaced, cup-shaped rotor mem- V bers 58 aresecured to what in a clutch is the output shaft and in a brake is theinput shaft. The magnetizable member forms an outer pole means andserves as a clutch input or a brake mounting member. The inner polemembers and the magnet are retained in an assembly, in the manner ofFIG. 4, by a press-fit sleeve. The poles 28 retain the non-magneticsleeve 71 that is provided with holes for the indexing adjustment. Oneindex hole is provided in member 70. The flux of magnet 32 links throughthe members 28, 58 and 70m develop a series-type magnetic field as shownby the broken lines and arrows. In this embodiment it will be noted thatthe polarity of the inner and outer poles differs for each of the rotors58.

From the foregoing it will be apparent that applicant has developed anextremely compact, reliable and substantially maintenance-free magneticclutch, which needs no outside electrical power source in order tooperate it, and which will not therefore be subject to heating up duringuse due to electric power. Moreover, the torque that is transmittable bythe clutch is readily adjustable in fine increments, merely by makingslight angular adjustments between the positions of the inner and outerpole teeth. Moreover, the magnetism developed in the driven rotor 58actually oscillates during rotation of the rotor so that, in effect, nosalient poles are developed in the rotor, and consequently undesirablecogging is eliminated. Furthermore, it has been found that by adjustingthe inner and outer poles angularly relative to one another aboutthecommon axis of the clutch, it is possible more accurately to controlincremental adjustments in the value of the transmittable torque.

FIG. 7 shows how by adjusting the collar 40, to shift the positions ofpoles 45 relative to poles 30, the per cent of transmittable torque maybe changed. In this FIG. the adjustment is such that the torquetransmitted is linear as indicated by the positions of the points X andX, on the curve. FIG. 7 shows also that the number of holes (A to O) incollar 40 may be different than the number (A to H) illustrated in FIGS.2 and 6 for smaller or larger adjustment increments.

While in the embodiment illustrated in FIGS; 1 and 2 sixteen angularlyspaced teeth have been employed in both the inner and outer polemembers, it will be understood that the exact number of teeth in eachmember can be varied without departing from this in. vention. It hasbeen found that the clutch or brake operates best when equally spacedpoles of equal width are employed. The dimensions of the air gapsbetween the inner and outer poles, and the annular portion 59 of therotor 58, may vary depending upon the application for which the clutchis designed.

Furthermore, while the invention has been described specifically inconnection with a clutch, it is to be understood, as stated, that it isequally applicable to brakes. Thus, in FIG. 1 if the shaft 26 isconsidered as, and is, stationary, the device will function as .a brakeoperating on shaft 14.

Having thus described my invention, what I claim is:

1. A magnetic slip torque device, comprising a rotatable output shaft,

a first magnetizable member rotatably mounted on said output shaft,

an outer pole member mounted on said first member for rotatableadjustment thereon about the axis of said output shaft,

said outer pole member having a plurality of internally projectingangularly spaced poles,

a rotatable, magnetizable inner pole member axially aligned with saidouter pole member and rotatably mounted on said output shaft, and havinga plurality of externally projecting angularly spaced poles, equal innumber to the number of poles on said outer pole member,

said outer poles surrounding said inner poles in radially spacedconfronting relation thereto, sand having a polarity different from saidinner poles so that magnetic flux lines extend between said inner andouter poles,

an annular permanent magnet rotatably mounted on said output shaftbetween said pole members in axial alignment therewith to rotate withsaid pole members and operative to develop a magnetic field between saidinner and outer poles,

a driven member secured to said output shaft and having an annularmagnetizable portion projecting into the radial space between said innerand outer poles and magnetically coupled to said poles, and

means for driving said first member,

said pole members being angularly adjustable relative to one anotherabout the axis of said output shaft to adjust the torque transmittableto said output shaft.

2. A magnetic slip torque device as claimed in claim 1, wherein saidfirst member, said permanent magnet, and said inner pole member arerotatal ly mounted on a 3. A magnetic slip torque device as defined inclaim 1 including a second plurality of inner, angularly spaced magneticpoles axially spaced from the first-named inner poles, and mounted torotate with said firstnamed inner poles coaxially of said common axis,

a second plurality of outer, angularly spaced magnetic poles surroundingsaid second plurality of inner poles in radially spaced confrontingrelation thereto, and mounted to rotate with said second plurality ofinner poles, and

a second driven member having a magnetizable annular portion projectinginto the radial space between said second pluralities of inner and outerpoles, respectively, thereby magnetically to be coupled to said secondpluralities of poles for rotation therewith about said common axis.

4. A magnetic slip torque device, comprising a drive member,

a driven member, and

means mounting said members for rotation relative to one another about acommon axis,

said drive member comprising a first plurality of poles angularly spacedabout said axis, and rotatable with said drive member,

a second plurality of angularly spaced poles surrounding said firstplurality in radially spaced confronting relation thereto, and rotatabletherewith, and

a permanent magnet secured to said drive member adjacent said firstplurality of poles and operative to develop a magnetic field betweensaid first and second pluralities of poles, respectively, and

said driven member having an annular, magnetizable portion projectinginto the radial space between said first and second pluralities of polesmagnetically to be coupled to said drive member, and

means for angularly adjusting one of said first and second pluralitiesof poles relative to the other about said axis thereby to adjust thetorque transmittable by said magnetic field from said drive to saiddriven member.

5. A magnetic slip torque device as defined in claim 4, wherein saidfirst plurality of poles are fixed to said drive member,

said second plurality of poles are carried by a ring,'

which surrounds said drive member and is angularly adjustable thereon,

said drive member has in its outer surface a reference hole, and

said ring has therethrough a plurality of angularly spaced radialopenings registrable selectively with said reference hole, upon angularadjustment of said ring on said drive member, said drive member beingoperative to transmit a different maximum torque to said driven memberwhen different openings in said ring are in registry with said referencehole.

6. A magnetic slip torque device as defined in claim 5, wherein saiddrive member has a circumferential groove in its outer surface beneathsaid ring, and

a setscrew is threaded through a radial opening in said ring and engagedat its inner end in said groove releasably to secure said ring againstrotation on said drive member.

7. A magnetic hysteresis type torque device, comprising a rotatabledrive member and a rotatable driven member,

one of said members having a first set of magnetizable poles angularlyspaced about its axis, and having a second set of magnetizable polesdisposed in operative relation to said first set of poles but spacedtherefrom,

the other of said members having a magnetizable part projecting into thespace between said first and second sets of poles,

a permanent magnet secured to one of said members to rotate therewith,and operative magnetically to couple said members, and

means for adjusting one of said sets of poles relative to the other setof poles about the axis of the member having the two sets of poles.

8. A magnetic hysteresis type torque device comprising a first rotatablemember having a plurality of angularly spaced magnetic poles,

a second member having a plurality of angularly spaced magnetic polesdisposed in confronting relation to the poles of said first member,

the poles of the two members having different polarity so that magneticflux lines extend between said members, and

means for angularly adjusting one of said members angularly relative tothe other about the axis of rotation of said first member, thereby tovary the .7 lit mit, and said device operating with composite eddycurrent and hysteresis torque in proportion to the slippage between saidmembers, the composite torque having the highest percentage of eddycurrents when the poles are aligned face to face.

1. A magnetic slip torque device, comprising a rotatable output shaft, afirst magnetizable member rotatably mounted on said output shaft, anouter pole member mounted on said first member for rotatable adjustmentthereon about the axis of said output shaft, said outer pole memberhaving a plurality of internally projecting angularly spaced poles, arotatable, magnetizable inner pole member axially aligned with saidouter pole member and rotatably mounted on said output shaft, and havinga plurality of externally projecting angularly spaced poles, equal innumber to the number of poles on said outer pole member, said outerpoles surrounding said inner poles in radially spaced confrontingrelation thereto, sand having a polarity different from said inner polesso that magnetic flux lines extend between said inner and outer poles,an annular permanent magnet rotatably mounted on said output shaftbetween said pole members in axial alignment therewith to rotate withsaid pole members and operative to develop a magnetic field between saidinner and outer poles, a driven member secured to said output shaft andhaving an annular magnetizable portion projecting into the radial spacebetween said inner and outer poles and magnetically coupled to saidpoles, and means for driving said first member, said pole members beingangularly adjustable relative to one another about the axis of saidoutput shaft to adjust the torque transmittable to said output shaft. 2.A magnetic slip torque device as claimed in claim 1, wherein said firstmember, said permanent magnet, and said inner pole member are rotatablymounted on a sleeve which is fixed to said output shaft, and said drivenmember is also fixed to said output shaft.
 3. A magnetic slip torquedevice as defined in claim 1, including a second plurality of inner,angularly spaced magnetic poles axially spaced from the first-namedinner poles, and mounted to rotate with said first-named inner polescoaxially of said common axis, a second plurality of outer, angularlyspaced magnetic poles surrounding said second plurality of inner polesin radially spaced confronting relation thereto, and mounted to rotatewith said second plurality of inner poles, and a second driven memberhaving a magnetizable annular portion projecting into the radial spacebetween said second pluralities of inner and outer poles, respectively,thereby magnetically to be coupled to said second pluralities of polesfor rotation therewith about said common axis.
 4. A magnetic slip torquedevice, comprising a drive member, a driven member, and means mountingsaid members for rotation relative to one another about a common axis,said drive member comprising a first plurality of poles angularly spacedabout said axis, and rotatable with said drive member, a secondplurality of angularly spaced poles surrounding said first plurality inradially spaced confronting relation thereto, and rotatable therewith,and a permanent magnet secured to said drive member adjacent said firstplurality of poles and operative to develop a magnetic field betweensaid first and second pluralities of poles, respectively, and saiddriven member having an annular, magnetizable portion projecting intothe radial space between said first and second pluralities of polesmagnetically to be coupled to said drive member, and means for angularlyadjusting one of said first and second pluralities of poles relative tothe other about said axis thereby to adjust the torque transmittable bysaid magnetic field from said drive to said driven member.
 5. A magneticslip torque device as defined in claim 4, wherein said first pluralityof poles are fixed to said drive member, said second plurality of polesare carried by a ring, which surrounds said drive member and isangularly adjustable thereon, said drive member has in its outer surfacea reference hole, and said ring has therethrough a plurality ofangularly spaced radial openings registrable selectively with saidreference hole, upon angular adjustment of said ring on said drivemember, said drive member being operative to transmit a differentmaximum torque to said driven member when different openings in saidring are in registry with said reference hole.
 6. A magnetic slip torquedevice as defined in claim 5, wherein said drive member has acircumferential groove in its outer surface beneath said ring, and asetscrew is threaded through a radial opening in said ring and engagedat its inner end in said groove releasably to secure said ring againstrotation on said drive member.
 7. A magnetic hysteresis type torquedevice, comprising a rotatable drive member and a rotatable drivenmember, one of said members having a first set of magnetizable polesangularly spaced about its axis, and having a second set of magnetizablepoles disposed in operative relation to said first set of poles butspaced therefrom, the other of said members having a magnetizable partprojecting into the space between said first and second sets of poles, apermanent magnet secured to one of said members to rotate therewith, andoperative magnetically to couple said members, and means for adjustingone of said sets of poles relative to the other set of poles about theaxis of the member having the two sets of poles.
 8. A magnetichysteresis type torque device comprising a first rotatable member havinga plurality of angularly spaced magnetic poles, a second member having aplurality of angularly spaced magnetic poles disposed in confrontingrelation to the poles of said first member, the poles of the two membershaving different polarity so that magnetic flux lines extend betweensaid members, and means for angularly adjusting one of said membersangularly relative to the other about the axis of rotation of said firstmember, thereby to vary the hysteresis of the device, to adjust thetorque transmitted between said members, said device operating withincipient hysteresis torque and zero slip when the load thereon does notexceed the torque which said members are adjusted to transmit, andoperating at continuous slip torque when the load on said device isequal to the torque which said members are adjusted to transmit, andsaid device operating with composite eddy current and hysteresis torquein proportion to the slippage between said members, the composite torquehaving the highest percentage of eddy currents when the poles arealigned face to face.